The present invention relates to a new and improved process for the further processing of the residue left behind in a crude oil refinery following vacuum distillation.
Following the final stage, performed under vacuum, of the fractionation distillation of crude oil in the refinery, those substances which do not volatilize up to approximately 550.degree. C. (normal pressure) are left behind in the distillation residue. As a function of the origin of the crude oil, this distillation residue generally corresponds to 25% of the crude oil infeed or feed. In practice, its further processing can take place by solvent treatment, e.g. by deasphalting by means of propane. As a result the residue is separated into a first fraction containing lubricating oils and waxes soluble in the solvent and a second fraction containing asphalts, asphaltenes, and so forth which are insoluble in the solvent. A larger quantity of the second fraction is obtained. Valuable non-fuels such as lubricating oils and waxes can be obtained from the first solution fraction, or they can be supplied to a cracker or cracking device for the recovery of low-boiling products. The second fraction or precipitate insoluble in the solvent is either used for bitumen production or in situ as a fuel for the refinery or, after admixing a lighter fraction for liquefaction purposes, as a heavier fuel outside the refinery, e.g. for power stations.
Various disadvantages and restrictions are inherent in processing the vacuum distillation residue or residue fraction by means of solvents. The lower-grade asphalt-containing fraction left behind in insoluble form after solvent treatment often corresponds to more than half the vacuum residue, which in the case of heavy crude oils can represent 40% or more of the crude oil. Such a large proportion exceeds the fuel requirements of the refinery. In connection with the second possible use of the insoluble fraction, i.e. bitumen production, problems also occur, because the asphalts and asphaltenes present in colloidal form in the crude oil are precipitated during solvent treatment. However, the indispensable complete redispersion necessary for bitumen production is often no longer possible, so that a low-grade product is obtained.
In addition, the solvent treatment does not completely dissolve the lubricating oil and wax fraction and instead high molecular components are dissolved and introduced into the first fraction which is disadvantageous for the end products obtained, e.g. leads to increased coking of the lubricating oils obtained therefrom.
Additionally, the use of low-boiling solvents calls for special safety measures and in particular expensive equipment. The recovery of the solvent is energy-consuming and due to the high solvent/residue ratio also costly.
European Patent No. 0,066,790, published Aug. 21, 1985, describes a process for the turbulent-film short-path vacuum distillation of the residue or residue fraction from an oil or petroleum refinery. Both the evaporation or vaporizing pressure and the temperature of the condensation surfaces decrease from infeed to residue removal. In order to improve the energy balance, the residue from vacuum distillation is fed to the short-path distillation process without any supply of energy, so that the heat of evaporation or vaporization of the feed, which has the residue temperature of the vacuum distillation residue, is removed, which necessarily leads to cooling and consequently to lower temperatures during short-path distillation than in the preceding vacuum distillation.
According to German Patent Publication No. 3,122,650, published Dec. 12, 1982, use is made of thin-film short-path vacuum distillation within an oil refinery, so that the crackable fraction or component yield is increased. Mechanical means like wipers are used to product a turbulent thin film. At the same time there is no need for accomplishing the conventional solvent extraction. The distillation temperature can be considerably lowered by lowering the operating pressure, which permits a careful distillation of fractions having a high atmospheric boiling point. The residue from the vacuum distillation preceding the short-path distillation is used for heating purposes, from which residue there is removed the heat of evaporation or vaporization, so that short-path distillation takes place at a temperature lower than that of the preceding vacuum distillation.